The present invention relates to a cutting tool and particularly to a milling cutting tool capable of performing face milling operations at a high feed rate and a long tool shank. The invention also discloses an indexable cutting insert for use with the cutting tool.
Japanese Publication No. 2000202703 A to Masaharu discloses a boring tool having two identical nearly parallelogrammatic plate form tips. Each tip has a pair of first cutting edges 15 and a pair of second cutting edges 16 arranged in a rotational symmetry and connected via a nose part 17. The first cutting edge 15 having a circular arcing cutting edge 15a at the side of the nose part 17 and a rectilinear cutting edge 15b merging with the cutting edge 15a via a first bending part 15. The second cutting edge 16 having two rectilinear cutting edges 16a and 16b merging via a second bending part 16c. 
Each of the tips used in ""703 is disposed differently with respect to the tool since each of the cutting edges has different characteristics. Since the cutting edges are arranged in 180xc2x0 rotational symmetry, each tip can be indexed only two times at its pocket. Furthermore, if the tips used in ""703 are used to perform ramp-down milling they are not properly supported against radially outwardly directed cutting forces that tend to withdraw each tip out of its pocket.
Japanese Publication No. 2000-005921 to Yoshimitsu shows, in FIG. 4 thereof, a three-corner cutting insert. Each of the three cutting edges comprises a small curved cutting edge portion 7 and a large straight cutting edge portion 8. The cutting insert of ""921 does not have a cutting edge specifically designed for performing ramp-down milling. Furthermore, the cutting insert is not properly supported against radially outwardly directed cutting forces that tend to withdraw the cutting insert out of its pocket during a ramp-down milling operation.
Another kind of tool, having means for preventing rotation of the cutting insert around the axis of the clamping screw, is shown in European Patent No. EP 0 091 408 B1 to Bylund. In ""408 there is disclosed a cutting insert 12 having three convex cutting edges 16, 17 and 18. Each of the cutting edges is connected, at a rear end thereof, to an auxiliary cutting edge 32, which extends transversely to the cutting edge and forms an obtuse angle therewith. The auxiliary cutting edge 32 is intended to cut the workpiece during reversed relative movement between the insert and the workpiece. The cutting edges of the cutting insert 12 are not peripherally continuous around the top face of the cutting insert. Instead, they are separated by an intermediate peripheral space 24, 25 and 26. The cutting insert 12 is not provided with a cutting edge for performing ramp-down milling operations and is not especially supported against radially outwardly directed cutting forces that tend to withdraw the cutting insert out of its pocket. For preventing rotation of the cutting insert, the cutting insert is provided with a supporting surface 27 that is directed substantially towards the center of the cutting insert. The supporting surface 27 abuts against an abutment surface 28 on the tool body that fits into the intermediate peripheral surface.
A disadvantage of the tool of ""408 is that in order to prevent rotation of the cutting insert, the cutting edges are formed with recesses which complicate and weaken the cutting insert.
It is an object of the present invention to provide a cutting tool and a cutting insert therefor that significantly reduce or overcome the aforementioned disadvantages.
In accordance with the present invention there is provided a cutting tool having a longitudinal axis, the cutting tool comprises a tool body, having at least one mounting leg formed at a front end thereof, the at least one mounting leg having an insert pocket with a cutting insert retained therein;
the insert pocket comprises a base wall and first and second rear sidewall sections transversely directed to the base wall, a generally circular recess extends downwardly from the base wall, the recess has a lower wall bounded by a peripheral wall extending uprightly from the lower wall to the base wall,
the cutting insert comprises an upper surface, a lower surface and a side surface extending therebetween, the upper and side surfaces intersecting at a cutting edge, a cylindrical protrusion having a cylindrical peripheral surface extends downwardly from the lower surface to a bottom surface of the protrusion;
wherein the cutting insert is retained in the insert pocket with first, second and third abutment surfaces of the insert pocket abutting the cutting insert, where the first abutment surface is located on the first rear sidewall section and it abuts a first support surface located on the side surface of the cutting insert, the second abutment surface is located on the second rear sidewall section and it abuts a second support surface located on the side surface of the cutting insert, and the third abutment surface is located on the peripheral wall of the recess and it abuts a third support surface located on the cylindrical peripheral surface of the protrusion of the cutting insert.
In accordance with a preferred embodiment of the present invention, the cutting edge comprises at least three cutting edge portions that are separated from each other by corner cutting edges and each cutting edge portion comprises a first cutting edge that extends between a second cutting edge and an adjacent corner cutting edge.
Preferably, the first cutting edge is convex.
If desired, the second cutting edge is straight.
Further in accordance with a preferred embodiment of the present invention, the side surface comprises side surface sections with a first side surface section adjacent the first cutting edge, a second side surface section adjacent the second cutting edge and a side surface corner section adjacent the corner cutting edge, each of the side surface sections extending from its associated cutting edge towards the lower surface.
In accordance with a preferred embodiment, the first and second rear sidewall sections are separated by a first recessed region.
Further in accordance with a preferred embodiment, the first support surface and the second support surface are located on either side of a common side surface corner section.
Typically, a portion of the common side surface corner section is located in the first recessed region.
Preferably, the peripheral wall of the recess comprises a major portion having a major radius, and a minor portion having a minor radius.
Further preferably, the minor radius is smaller than the major radius.
Still further preferably, the angular extent of the minor portion is smaller than the angular extent of the major portion.
In accordance with a preferred embodiment, a threaded bore extends downwardly from the lower wall of the recess.
Typically, a through bore, having an insert axis, extends between the upper surface of the cutting insert and the bottom surface of the protrusion.
Further typically, a retaining screw is located in the through bore and threadingly engages the threaded bore.
In accordance with a specific embodiment of the present invention, first cutting edge subtends a first angle (xcex1) of 70xc2x0 with the insert axis.
Further in accordance with a specific embodiment of the present invention, the second cutting edge subtends a second angle (xcex2) of 35xc2x0 with the insert axis.
Typically, the first cutting edge forms an obtuse interior third angle (xcex3) with the adjacent second cutting edge.
In accordance with a specific embodiment of the present invention, the third angle is 153xc2x0.
Also in accordance with the present invention there is provided a cutting insert, comprising an upper surface, a lower surface; and a side surface extending between the upper and lower surfaces with the upper and side surfaces intersecting at a cutting edge; a cylindrical protrusion having a cylindrical peripheral surface extending downwardly from the lower surface to a bottom surface of the protrusion, the cutting insert having an insert axis passing through the upper and bottom surfaces;
wherein the cutting edge comprises at least three cutting edge portions that are separated from each other by corner cutting edges, each cutting edge portion comprising a first convex cutting edge that extends between a second cutting edge and an adjacent corner cutting edge.
If desired, the second cutting edge is straight.
In accordance with a specific embodiment of the present invention, first cutting edge subtends a first angle (xcex1) of 70xc2x0 with the insert axis.
Further in accordance with a specific embodiment of the present invention, the second cutting edge subtends a second angle (xcex2) of 35xc2x0 with the insert axis.
Typically, the first cutting edge forms therewith an obtuse interior third angle (xcex3) with the adjacent second cutting edge.
In accordance with a specific embodiment of the present invention, the third angle is 153xc2x0.
Typically, a through bore, having as axis the insert axis, extends between the upper surface of the cutting insert and the bottom surface of the protrusion.